The present invention relates to an interface switching apparatus and a switching control method wherein a plurality of information processing systems (hereinafter referred to as the hosts) having a serial interface capable of dynamic insertion and removal can share at least a peripheral device (hereinafter referred to as the device) having the same serial interface. The present invention also relates to a device which can be shared by a plurality of hosts. The present invention further relates to the interface switching apparatus and the switching control method in which a USB (Universal Serial Bus) is applied to the serial interface.
The use of the USB is extending as a serial interface for connecting the peripheral units (devices) such as a keyboard and a mouse to the information processing systems (hosts).
The USB specification is briefly described in xe2x80x9cUNIVERSAL SERIAL BUS SPECIFICATION version 1.0 (Jan. 15, 1996), pp.27-28, available from the U.S. USB Implementers Forum (URL on internet is http://www.usb.org/).
Each USB host is basically connected with one USB device. The use of a USB hub having the port repeater function, however, makes it possible to connect a plurality of USB devices to each USB host.
In addition to USB, a serial interface called IEEE1394 is finding applications. IEEE1394, like USB, is capable of dynamic insertion and removal and can be added through a hub. The data transfer rate of the USB is about 12 MBits/sec at maximum, whereas IEEE1394 specified by IEEE has a data transfer rate as high as 400 MBits/sec.
In recent years, a system called xe2x80x9ca clusterxe2x80x9d is extending as a system for improving the reliability of information processing systems, in which each of a plurality of information processing systems monitors the operations of the other information processing systems and ready to switch various processes to a normal system in case of a fault. The cluster system is configured of a plurality of servers, and in order to reduce the installation space, the devices such as the monitors, the keyboards and the mice (hereinafter referred to as xe2x80x9cthe console devicesxe2x80x9d) are desirably shared in use.
Conventional means for sharing the console devices is switching a monitor signal or a keyboard signal by a switch. The journal xe2x80x9cASCII/V, March Issuexe2x80x9d published by ASCII in February 1996, p. 192 discloses a keyboard switch for performing a switching operation by depressing a specified combination of keys on the keyboard.
Among the various console devices, the interfaces of the keyboard and the mouse have been increasingly using the USB. According to the USB specification, however, connection of a device to a plurality of USB hosts is not permitted. For a given USB bus, for example, only one USB host can exist at a time.
The first problem, therefore, is that in sharing a console among a cluster system or among a plurality servers, a USB console device such as a keyboard or a mouse cannot be connected to a plurality of hosts at a time.
A possible solution to this method is to switch the route of connection between a USB device and a USB host by normal switching means as in the prior art. In the USB, however, the dynamic insertion and removal function requires the process of disconnecting and connecting the USB signal each time the switch is operated. As in the normal dynamic insertion and removal operation, therefore, a hardware reset control of a device is executed based on the USB specification. The second problem is that a simple switching circuit consumes a considerable time before a USB device becomes usable each time of switching by the hardware reset operation accompanying the dynamic insertion and removal operation.
The third problem is that the switching of a console has no relation with the main host of a cluster system in the conventional interface switching means using the manual switching operation. In the case where a fault is detected in a given host, for example, the console cannot be switched in response to the fail-over (the operation of switching a process at the time of a fault) of the cluster to inform the manager of the fault quickly.
The fourth problem is that if the operation of the interface switching means is to be interlocked with a fail-over of a cluster, the host is required to perform the switching control operation using a different control signal in view of the fact that the conventional keyboard interface lacks any specification of communicating such a switching command.
The fifth problem of the conventional manual interface switching means is that even an input not connected to a host could be selected. In a system constituting a three-input switch having only two hosts, for example, nothing is displayed on the monitor when switched to the remaining one input so that a keyboard entry is invalid very inconveniently in the absence of a host to communicate with. The user is required to be always conscious of this limitation.
The sixth problem is that if a USB switch obviating the first or second problem described above is available, a monitor signal as well as the keyboard and the mouse is actually required to be switched. The monitor signal, however, is a video signal or governed by the IEEE1394 specification described above and requires a different interface switching means.
The seventh problem is that when a given USB keyboard is connected to another USB host having a different architecture using some switching means, the switching of the key code is required.
A first object of the present invention is to provide a USB switching apparatus, and a USB device which can be connected to a plurality of USB hosts and thus can be shared among a plurality of the USB hosts.
A second object of the invention is to provide a USB switching apparatus which can reduce the time required before a USB device becomes usable after starting to switch the USB.
A third object of the invention is to provide a USB switching apparatus which can switch the connection of a USB host in response to an command from the host in the case where a fault occurs in the USB host in a cluster configuration or the like.
A fourth object of the invention is to provide a USB switching apparatus in which a switching command can be issued from a USB host without any new control interface between the USB host and the USB switching apparatus.
A fifth object of the invention is to provide a USB switching apparatus in which the connection is not switched to a connection system with which any USB host is not connected.
A sixth object of the invention is to provide the USB switching apparatus described above, which is capable of switching the interfaces other than the USB at the same time.
A seventh object of the invention is to provide a USB keyboard capable of being connected to a USB host of a different architecture.
In order to achieve the above-mentioned objects, the present invention comprises the means described below.
The means for solving the first problem is a USB switch having an interface with a plurality of USB hosts, in which an arbitrary one of the USB hosts is selected to establish a connection route with a USB device.
The means for solving the second problem is a USB switch having an interface with a plurality of USB hosts, configured in such a manner that during the period when a connection route established between an arbitrary host and a device is switched to another arbitrary host, the device continues to be supplied with power and the host with which a connection is to be newly established is supplied with the same signal as when the device is attached dynamically. Specifically, the device continues to be supplied with power and therefore is not reset when the host is switched. Also, the host can recognize the switching of the device correctly by receiving a pseudo-dynamic insertion signal.
The means for solving the fourth problem is configured in such a manner that a switching control command is issued from a host to a USB switch which receives the switching control command as a USB device for performing the switching operation. As a result, the host can freely control the connection route, and a new control signal is not required to be added for connecting the host and the USB switch.
The third problem can be solved by the host issuing the above-mentioned switching control command upon detection of a fault in the cluster control software.
The means for solving the fifth problem is so configured that the host-side interface of a USB switch recognizes a host-side connection or the switching power on, and the switching control of a host is invalidated in the case where the connection is not established or power is not supplied on host side.
The means for solving the sixth problem is configured in such a manner that the host switching control signal for the USB switch is used also for switching other interfaces.
The means for solving the seventh problem is configured in such a manner that a key code table is provided in the USB keyboard and switched according to the architecture of the USB host connected.